1. Field of the Invention
This invention relates to mechanisms for applying screen-printed decorations to clothing and more particularly to a base or pallet for supporting shirts in a screen-printing machine.
2. Background Information
Printed T-shirts and other clothing items remain a popular consumer item. Printed decorations, in the form of printed logos, patterns, and text, are often applied to shirts using a version of the well-known screen-printing technique. FIG. 1 shows a modem high-volume screen-printing device 100 that employs a rotating carousel 102 and a plurality of individual processing stations 104 arranged in a circle. The illustrated example shows a conventional commercially available screen-printing device having eighteen separate stations/rotary positions. The exemplary device is Challenger II(trademark) available from M and R Sales and Service, Inc. of Glen Ellyn, Ill.
In general, the screen printing technique uses a stencil with perforations (e.g. a xe2x80x9cscreenxe2x80x9d) that match the pattern to be applied to the shirt. The shirt is mounted on a pallet (a rubberized, flat and heat-resistant surface) and passed under the pattern. A squeegee device above the pattern forces colored ink through the perforations, onto the shirt. The paint penetrates the pores of the cloth sufficiently to become permanent under normal wear, and is formulated with a viscosity and flow that prevents excessive bleeding through the cloth or under the screen. The applied paint is then dried at a drying station using a heater and the shirt is either removed or passed to another screen for application of further printing in, for example, another color. Each color is applied and dried in turn. An exemplary screen printing station 108 for the mechanism 100 is shown.
In the exemplary mechanism, a set of pallets 114 are each mounted on carousel arms 115 that extend radially outwardly from the central revolving hub 116. The pallets are advanced/indexed with respect to each of the stations 104 at a constant rate as they pass from loading to printing of the design 121 (one or several colors), and finally to drying and unloading (see unloading worker 117).
Initial placement of the item-to-be-printed on the pallet 114 is quite critical. In the illustrated example of a screen-printed T-shirt 112, if a shirt is not well centered, then the printing will appear crooked or offset, and the finished shirt is defective. Typically, a worker 109 (standing at the loading station 110) must quickly overlay and seat the shirt front 119 on the pallet 114 by hand in a manner that is accurately centered. Centering (e.g. xe2x80x9cregistrationxe2x80x9d) typically entails the placement of the shirt so that the collar 120 is near the outer-facing edge 118 of the pallet, and the arm seams 122 are evenly spaced from the two opposing pallet side edges 124.
As shown, where the pallet is not well sized to the shirt, the arm seams 122 are draped at a significant distance DA from the pallet side edges 124. In many cases DA can be several inches (where large-sized shirts are printed). This increases the difficulty for the worker to properly judge the center of the shirt while he or she loads it onto the palletxe2x80x94particularly at a desired operating speed, which can be 450-600 shirts per hour.
A variety of centering/registration mechanisms exist to ease the difficulty of properly loading pallets, but these often involve complex machine vision and optical solutions that are neither cost-effective nor easy to use, particularly by an unskilled operator. As such, manual solutions and the human eye are often preferred.
As shown in FIG. 2, one proven manual solution is to provide a set 150 of differently sized pallets representing desired increments of size change (from Small (S) to Extra-Extra-Extra-Large (XXXL), for example). These can be changed-out on each arm 115 as needed as represented by the arrows 160. Each arm includes an appropriate bracket and locking mechanism (not shown) for mounting and securing the pallet. Pallets are slid onto and off the arm (double arrow 161) when a change is made. However, maintaining multiple sets of differently sized pallets for each machine is costly (currently over $100 per pallet). It is also impractical to maintain a pallet for each size. In the example of FIG. 2, the set 150 consists of a small medium and large pallet 152, 154 and 156, respectively. These have respective widths W1, W2 and W3 that vary by several inches (for example W1=16 inches; W2=20 inches and W3=24 inches). However the use of multiple pallet sizes may still not guarantee close centering of all possible sizes. It is recognized that the width of the pallet should increase approximately xc2xe to 1 inch for each increased shirt size. Therefore, certain sizes are simply loaded on a smaller-size pallet. This often leads to higher reject rates with these xe2x80x9cin-betweenxe2x80x9d sizes since the gap between the pallet side edges and the sleeve seams is increased beyond the desired minimum distance.
A significant disadvantage to using a plurality of differently sized pallets to accommodate various shirt sizes is that the change-out of a full set of pallets is typically time-consuming. Each time a size change is needed, the old pallets must be removed from their support beams and stacked or placed aside, the new pallets must then be unstacked and then mounted on the beams.
Accordingly, it is desirable to provide a pallet or base for screen-printing devices that accommodates a wide range of sizes without requiring differently sized pallet sets or a time-consuming change-out process. The pallet should fit readily on existing device supports and provide a rapidly adjustable mechanism for accommodating different sizes. The pallet should provide for easy and accessible adjustment and should exhibit desired weight and heat-dissipation characteristics so as to be compatible with existing devices and components. It should also enhance the operator""s ability to rapidly and accurately center clothing pieces thereon.
This invention overcomes the disadvantages of the prior art by providing a base or pallet that is variably adjustable along its width to specifically accommodate a wide range of differently sized pieces of clothing. A main pallet base is flanked by a pair of extendable and retractable (movable) wings, along the underside thereof, that are constructed from a durable material and that extend simultaneously in opposing directions.
In an illustrative embodiment, a movement-balancing mechanism, such as a rack-and-pinion assembly or pantograph, is used to extend and retract the wings at a similar rate. In this manner, pulling or pushing on one wing causes the other to move simultaneously through the operatively connected rotation of the pinion assembly. The wings are locked in place using a locking mechanism beneath the outer-facing side of the main base. The locking mechanism can be a block that applies friction to one of the rack sets of the rack-and-pinion assembly or other movement-balancing mechanism. The clothing piece, when loaded, draped from the side edges of the main base onto the wings, and whence over the side edges of the wings. The side edges are set so as to be adjacent to the sleeve seams, or other desired center-registration points, on the clothing piece.
In an illustrative embodiment, the pair of movable wings are each sized and arranged to be retractable to a position fully beneath the underside so as to be free of extension beyond the opposing side edges. The wings are provided with graduations that are referenced against the respective main base side edges or another indicia. The graduations are chosen to relate to the sizes that are accommodated by the pallet so that adjustment to the wings can be made without needing to fit the shirt to the pallet first. To assist in guiding the wings linearly, a set of slots are provided in the wings that ride over guide screws and sleeves that are secured to the bottom of the main base. The wings can also be provided with enlarged central cutouts to reduce weight and heat buildup.